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/* Copyright (C) 1995, 1996 Aladdin Enterprises.  All rights reserved.

  This software is provided AS-IS with no warranty, either express or

  implied.

  This software is distributed under license and may not be copied,

  modified or distributed except as expressly authorized under the terms

  of the license contained in the file LICENSE in this distribution.

  For more information about licensing, please refer to

  http://www.ghostscript.com/licensing/. For information on

  commercial licensing, go to http://www.artifex.com/licensing/ or

  contact Artifex Software, Inc., 101 Lucas Valley Road #110,

  San Rafael, CA  94903, U.S.A., +1(415)492-9861.

*/

/* $Id: gdevstc4.c,v 1.4 2002/02/21 22:24:52 giles Exp $*/

/* Epson Stylus-Color Printer-Driver */

/***

     This file holds a byte-Implementation of the Floyd-Steinberg error

     diffusion-algorithm. This algorithm is an alternative for high quality 

     printing in conjunction with the PostScript-Header stcolor.ps:

          gs -sDEVICE=stcolor -sDithering=fs2 <other options> stcolor.ps ...

     THIS ALGORIHM WAS WRITTEN BY STEVEN SINGER (S.Singer@ph.surrey.ac.uk)

     AS PART OF escp2cfs2. 

     THIS IMPLEMENTATION INCORPORATES ONLY FEW CHANGES TO THE ORIGINAL CODE.

 ***/

#include "gdevstc.h"

/*

 * escp2c_pick best scans for best matching color 

 */

private byte *

escp2c_pick_best(byte *col)

{

    static byte colour[8][3] = {

       {  0,  0,  0},{255,  0,  0},{  0,255,  0},{255,255,  0},

       {  0,  0,255},{255,  0,255},{  0,255,255},{255,255,255}};

    register int x, y, z, dx, dy, dz, dz2, dx2, dx3, dx4;

    register byte *p;

    register long md, d;

    md = 16777216; /* plenty */

/*

   Note that I don't use a simple distance algorithm. That can lead to a block

   of (130,127,127) being dithered as red-cyan. This algorithm should make

   it use black-white-red. This is very important, as a coloured block in

   the middle of a grey block can, via error diffusion, perturb the

   surrounding colours sufficiently for this to happen.

*/

/*

   The next bit is equivalent to this, but faster.

    x = col[0];

    y = col[1];

    z = col[2];

    for(n=8; n--; )

    {

	dx = x - colour[n][0];

	dy = y - colour[n][1];

	dz = z - colour[n][2];

	d = dx*(dx-(dy>>1)) + dy*(dy-(dz>>1)) + dz*(dz-(dx>>1));

	if (d < md)

	{

	    md = d;

	    p = n;

	}

    }

*/

/*

 * Test colours in gray code order to reduce number of recalculations.

 * I bet you can't find an optimiser that would do this automatically.

 */

    x = col[0];

    y = col[1];

    z = col[2];

    dx = x*(x-(y>>1));

    dy = y*(y-(z>>1));

    dz = z*(z-(x>>1));

    md = dx + dy + dz;

    p = colour[0];

    x -= 255;

    dx2 = x*(x-(y>>1));

    dz2 = z*(z-(x>>1));

    if ((d = dx2 + dy + dz2) < md) {md = d; p = colour[1];}

    y -= 255;

    dx3 = x*(x-(y>>1));

    dy = y*(y-(z>>1));

    if ((d = dx3 + dy + dz2) < md) {md = d; p = colour[3];}

    x += 255;

    dx4 = x*(x-(y>>1));

    if ((d = dx4 + dy + dz) < md) {md = d; p = colour[2];}

    z -= 255;

    dy = y*(y-(z>>1));

    dz = z*(z-(x>>1));

    if ((d = dx4 + dy + dz) < md) {md = d; p = colour[6];}

    x -= 255;

    dz2 = z*(z-(x>>1));

    if ((d = dx3 + dy + dz2) < md) {md = d; p = colour[7];}

    y += 255;

    dy = y*(y-(z>>1));

    if ((d = dx2 + dy + dz2) < md) {md = d; p = colour[5];}

    if ((d = dx + dy + dz) < md) {p = colour[4];}

    return(p);

}

/*

 * escp2c_conv_stc converts into the ouput format used by stcolor

 */

private void

escp2c_conv_stc(byte *p, byte *q, int i)

{

    for(; i; p+=3, i-=3)

        *q++ = (*p & RED) | (p[1] & GREEN) | (p[2] & BLUE);

}

/*

 * Limit byte-values

 */

#define LIMIT(a) if (a > 255) a = 255; if (a < 0) a = 0

#define LIMIT2(a) if (a > 127) a = 127; if (a < -128) a = -128; \

                if (a < 0) a += 256

/*

 * Main routine of the algorithm

 */

int 

stc_fs2(stcolor_device *sd,int npixel,byte *in,byte *buf,byte *out)

{

   int fullcolor_line_size = npixel*3;

/* ============================================================= */

   if(npixel > 0) {  /* npixel >  0 -> scanline-processing       */

/* ============================================================= */

/*    -------------------------------------------------------------------- */

      if(in == NULL) { /* clear the error-buffer upon white-lines */

/*    -------------------------------------------------------------------- */

         memset(buf,0,fullcolor_line_size);

/*    ------------------------------------------------------------------- */

      } else {                 /* do the actual dithering                 */

/*    ------------------------------------------------------------------- */

    int i, j, k, e, l, i2, below[3][3], *fb, *b, *bb, *tb;

    byte *p, *q, *cp;

    static int dir = 1;

    p = buf;

    if (*p != 0 || memcmp((char *) p, (char *) p + 1, fullcolor_line_size - 1))

    {

	for(p = in, q=buf, i=fullcolor_line_size;

	    i--; p++, q++ )

	{

	    j = *p + ((*q & 128) ? *q - 256 : *q);

	    LIMIT(j);

	    *p = j;

	}

    }

    p = in;

	fb = below[2];

	b = below[1];

	bb = below[0];

	*b = b[1] = b[2] = *bb = bb[1] = bb[2] = 0;

	if (dir)

	{

	    for(p = in, q=buf-3,

		i=fullcolor_line_size; i; i-=3)

	    {

		cp = escp2c_pick_best(p);

		for(i2=3; i2--; p++, q++, fb++, b++, bb++)

		{

		    j = *p;

		    *p = *cp++;

		    j -= *p;

		    if (j != 0)

		    {

			l = (e = (j>>1)) - (*fb = (j>>4));

			if (i > 2)

			{

			    k = p[3] + l;

			    LIMIT(k);

			    p[3] = k;

			}

			*b += e - (l = (j>>2) - *fb);

			if (i < fullcolor_line_size)

			{

			    l += *bb;

			    LIMIT2(l);

			    *q = l;

			}

		    }

		    else

			*fb = 0;

		}

		tb = bb-3;

		bb = b-3;

		b = fb-3;

		fb = tb;

	    }

	    *q = *bb;

	    q[1] = bb[1];

	    q[2] = bb[2];

	    dir = 0;

	}

	else

	{

	    for(p = in+fullcolor_line_size-1,

		q = buf+fullcolor_line_size+2, i=fullcolor_line_size; 

                i; i-=3)

	    {

		cp = escp2c_pick_best(p-2) + 2;

		for(i2=3; i2--; p--, q--, fb++, b++, bb++)

		{

		    j = *p;

		    *p = *cp--;

		    j -= *p;

		    if (j != 0)

		    {

			l = (e = (j>>1)) - (*fb = (j>>4));

			if (i > 2)

			{

			    k = p[-3] + l;

			    LIMIT(k);

			    p[-3] = k;

			}

			*b += e - (l = (j>>2) - *fb);

			if (i < fullcolor_line_size)

			{

			    l += *bb;

			    LIMIT2(l);

			    *q = l;

			}

		    }

		    else

			*fb = 0;

		}

		tb = bb-3;

		bb = b-3;

		b = fb-3;

		fb = tb;

	    }

	    *q = *bb;

	    q[1] = bb[1];

	    q[2] = bb[2];

	    dir = 1;

	}

    escp2c_conv_stc(in, out, fullcolor_line_size);

/*    ------------------------------------------------------------------- */

      }                        /* buffer-reset | dithering                */

/*    ------------------------------------------------------------------- */

/* ============================================================= */

   } else {          /* npixel <= 0 -> initialisation            */

/* ============================================================= */

/*

 * check wether the number of components is valid

 */

      if(sd->color_info.num_components != 3)                       return -1;

/*

 * check wether stcdither & TYPE are correct

 */

      if(( sd->stc.dither                    == NULL) ||

         ((sd->stc.dither->flags & STC_TYPE) != STC_BYTE))         return -2;

/*

 * check wether the buffer-size is sufficiently large

 */

      if((sd->stc.dither->flags/STC_SCAN) < 1)                     return -3;

/*

 * finally clear the buffer

 */

      memset(buf,0,-fullcolor_line_size);

/* ============================================================= */

   } /* scanline-processing or initialisation */

/* ============================================================= */

   return 0;

}